Adding Deprecation Warning For hash_type

[ericspod]

Description

Addresses missing deprecation warnings about the changing default value of hash_type in #9088. The solution in #9124 isn't ideal since the warning comes up in too many scenarios, the objective is to raise the warning when no value is passed explicitly to let users know to change things, and at the same time not breaking backwards compatibility. The behaviour defaults to using md5 as the hash_type, perhaps it's more secure for this to be sha256 despite compatibility breaking?

There's also one minor MLFlow test fix.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

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📝 Walkthrough

download_url, extractall, and download_and_extract now default hash_type to None. When hash_val is provided without hash_type, download_url and extractall warn and use SHA-256. Tests check both warning paths. Documentation describes the default.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~12 minutes

Merge Risk: ⚪ Minimal · up to 3d9c9

The checksum fallback remains SHA-256 when no algorithm is specified, while inspected MD5 paths select MD5 explicitly. The change adds the intended warning without a demonstrated checksum regression.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 87.50% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 3 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the main change: adding a deprecation warning for the changing hash_type default.
Description check	✅ Passed	The description explains the motivation, compatibility behavior, related issue, and minor test fix. It includes the required Description and Types of changes sections. The template issue line is missi…

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Actionable comments posted: 1

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Inline comments:
In `@monai/apps/utils.py`:
- Line 255: Update the deprecation warning messages in both functions that
default hash_type to "sha256" so they state “Defaulting to sha256 checking”
instead of MD5, and update both corresponding tests to assert the SHA-256
wording.

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• tests/apps/test_download_and_extract.py

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[garciadias]

Thanks @ericspod, warning only when hash_val is given and hash_type isn't is the right trigger, and download_and_extract doesn't double-warn (extractall is called without hash_val). Some points:

1. Version history in the messages is inaccurate. sha256 became the default in 1.6.1 (#9088, already released, with no warning), and None arrives with this PR, so in 1.6.2/1.7, not 1.6.1. The warning text and the three versionchanged:: 1.6.1 blocks say "changed to None from md5 in 1.6.1". check_hash's note ("md5 -> sha256 in 1.6.1") is the accurate one. Suggest: "changed from md5 to sha256 in 1.6.1; from the default is None, which warns and uses sha256".
2. Compatibility is still broken for the users this targets. Someone on <=1.6.0 code passing an MD5 hash_val without hash_type now gets the FutureWarning and then HashCheckError, because it still checks sha256. I verified this locally with extractall. Since MD5 (32 hex chars) and SHA-256 (64) are distinguishable by length, you could infer md5 when len(hash_val) == 32 and warn. That restores the pre-1.6.1 behaviour without silently weakening anything for a 64-char hash. This would also answer the sha256-vs-md5 question in the description: keep sha256 as the default, accept legacy MD5 only when the value can only be MD5.
3. Warning location. warn_deprecated uses stacklevel=2, so the warning points at monai/apps/utils.py rather than the caller's code. A direct warnings.warn(..., FutureWarning, stacklevel=2) (or 3 through wrappers) would show users where to add hash_type.
4. Tests. The new assertWarns checks are inside @skip_if_quick network tests. A small offline test would run in the quick suite: local tarball + extractall, asserting it warns with no hash_type, doesn't warn with hash_type set, and doesn't warn without hash_val.

The MLflow test fix ("md5" passed explicitly) LGTM. tests/apps/test_download_and_extract.py: 13 passed locally; CI green.

[ericspod]

Hi @garciadias I can fix the version problem, this was supposed to be in for 1.6.1, and the warning stack level. By backwards compatibility I meant the function default values for hash_type are now None but this is equivalent to sha256 as previously merged. If we look at the hash's length to choose md5 then we're changing what the solution for the security alert we published. I think the tests with added checks for the future warning will run before merging so I don't think they're a priority to run in a quick test. The quick tests are for testing a lot more high level functionality locally.